1. Field of Invention
The present invention relates to an inspection method. More particularly, the present invention relates to a method of inspecting a photomask defect.
2. Description of Related Art
In the fabrication of integrated circuits, a pattern on a wafer or the various types of material layer on the wafer is formed by a transfer from a photomask pattern. A typical approach is to form a photoresist layer on a wafer, followed by projecting the pattern of the photomask on the photoresist layer via an exposure process. Thereafter, a development process is performed to the required pattern in the photoresist layer. With a subsequent etching process, the pattern in the photoresist layer is transferred to the wafer or the material layer on the wafer.
As the device dimension continues to reduce and integrated circuits become more complicated, it is important to form an accurate pattern on a photomask. The current fabrication techniques of a photomask can not assure the formation of a perfect photomask without defects. Unfortunately, defects are normally present in a newly fabricated photomask; thus, it is necessary to inspect the photomask to determine whether it is acceptable for used, or a repair or a remake of the photomask is required. On the other hand, even the photomask is acceptable for use, it is necessary to subject the photomask to an inspection prior to its use in the patterning of a wafer to ensure the stability of the process and to obviate defects being generated during the process to affect the accuracy of the to-be-formed pattern.
A typical method of inspecting defects on a photomask includes actually forming a photoresist layer on a wafer, followed by performing an exposure-and-development process to transfer the pattern from the photomask to a photoresist layer. Then, by evaluating the pattern in the photoresist layer to determine whether the photomask passes the inspection. However, the conventional approach is very time-consuming and non-economical.